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28 .\" @(#)icmp.4 8.1 (Berkeley) 6/5/93
36 .Nd Internet Control Message Protocol
42 .Fn socket AF_INET SOCK_RAW proto
45 is the error and control message protocol used
48 and the Internet protocol family.
52 for network monitoring
53 and diagnostic functions.
56 parameter to the socket call to create an
60 .Xr getprotobyname 3 .
62 sockets are connectionless,
63 and are normally used with the
69 call may also be used to fix the destination for future
70 packets (in which case the
78 system calls may be used).
80 Outgoing packets automatically have an
83 them (based on the destination address).
84 Incoming packets are received with the
86 header and options intact.
88 ICMP messages are classified according to the type and code fields
89 present in the ICMP header.
90 The abbreviations for the types and codes may be used in rules in
92 The following types are defined:
93 .Bl -column x xxxxxxxxxxxx -offset indent
94 .It Sy Num Ta Sy Abbrev. Ta Sy Description
95 .It 0 Ta echorep Ta "Echo reply"
96 .It 3 Ta unreach Ta "Destination unreachable"
97 .It 4 Ta squench Ta "Packet loss, slow down"
98 .It 5 Ta redir Ta "Shorter route exists"
99 .It 6 Ta althost Ta "Alternate host address"
100 .It 8 Ta echoreq Ta "Echo request"
101 .It 9 Ta routeradv Ta "Router advertisement"
102 .It 10 Ta routersol Ta "Router solicitation"
103 .It 11 Ta timex Ta "Time exceeded"
104 .It 12 Ta paramprob Ta "Invalid IP header"
105 .It 13 Ta timereq Ta "Timestamp request"
106 .It 14 Ta timerep Ta "Timestamp reply"
107 .It 15 Ta inforeq Ta "Information request"
108 .It 16 Ta inforep Ta "Information reply"
109 .It 17 Ta maskreq Ta "Address mask request"
110 .It 18 Ta maskrep Ta "Address mask reply"
111 .It 30 Ta trace Ta Traceroute
112 .It 31 Ta dataconv Ta "Data conversion problem"
113 .It 32 Ta mobredir Ta "Mobile host redirection"
114 .It 33 Ta ipv6-where Ta "IPv6 where-are-you"
115 .It 34 Ta ipv6-here Ta "IPv6 i-am-here"
116 .It 35 Ta mobregreq Ta "Mobile registration request"
117 .It 36 Ta mobregrep Ta "Mobile registration reply"
118 .It 39 Ta skip Ta SKIP
119 .It 40 Ta photuris Ta Photuris
122 The following codes are defined:
123 .Bl -column x xxxxxxxxxxxx xxxxxxxx -offset indent
124 .It Sy Num Ta Sy Abbrev. Ta Sy Type Ta Sy Description
125 .It 0 Ta net-unr Ta unreach Ta "Network unreachable"
126 .It 1 Ta host-unr Ta unreach Ta "Host unreachable"
127 .It 2 Ta proto-unr Ta unreach Ta "Protocol unreachable"
128 .It 3 Ta port-unr Ta unreach Ta "Port unreachable"
129 .It 4 Ta needfrag Ta unreach Ta "Fragmentation needed but DF bit set"
130 .It 5 Ta srcfail Ta unreach Ta "Source routing failed"
131 .It 6 Ta net-unk Ta unreach Ta "Network unknown"
132 .It 7 Ta host-unk Ta unreach Ta "Host unknown"
133 .It 8 Ta isolate Ta unreach Ta "Host isolated"
134 .It 9 Ta net-prohib Ta unreach Ta "Network administratively prohibited"
135 .It 10 Ta host-prohib Ta unreach Ta "Host administratively prohibited"
136 .It 11 Ta net-tos Ta unreach Ta "Invalid TOS for network"
137 .It 12 Ta host-tos Ta unreach Ta "Invalid TOS for host"
138 .It 13 Ta filter-prohib Ta unreach Ta "Prohibited access"
139 .It 14 Ta host-preced Ta unreach Ta "Precedence violation"
140 .It 15 Ta cutoff-preced Ta unreach Ta "Precedence cutoff"
141 .It 0 Ta redir-net Ta redir Ta "Shorter route for network"
142 .It 1 Ta redir-host Ta redir Ta "Shorter route for host"
143 .It 2 Ta redir-tos-net Ta redir Ta "Shorter route for TOS and network"
144 .It 3 Ta redir-tos-host Ta redir Ta "Shorter route for TOS and host"
145 .It 0 Ta normal-adv Ta routeradv Ta "Normal advertisement"
146 .It 16 Ta common-adv Ta routeradv Ta "Selective advertisement"
147 .It 0 Ta transit Ta timex Ta "Time exceeded in transit"
148 .It 1 Ta reassemb Ta timex Ta "Time exceeded in reassembly"
149 .It 0 Ta badhead Ta paramprob Ta "Invalid option pointer"
150 .It 1 Ta optmiss Ta paramprob Ta "Missing option"
151 .It 2 Ta badlen Ta paramprob Ta "Invalid length"
152 .It 1 Ta unknown-ind Ta photuris Ta "Unknown security index"
153 .It 2 Ta auth-fail Ta photuris Ta "Authentication failed"
154 .It 3 Ta decrypt-fail Ta photuris Ta "Decryption failed"
156 .Ss MIB (sysctl) Variables
159 protocol implements a number of variables in the
163 MIB, which can also be read or modified with
165 .Bl -tag -width ".Va icmplim_output"
168 Enable/disable ICMP replies received via broadcast or multicast.
172 Enable/disable dropping of ICMP Redirect packets.
176 Bandwidth limit for ICMP replies in packets/second.
177 If set to zero, no limiting will occur.
179 .It Va icmplim_output
181 Enable/disable logging of ICMP replies bandwidth limiting.
185 Enable/disable logging of ICMP Redirect packets.
188 .Pq Vt "unsigned integer"
191 is set and this value is non-zero,
192 it will be used instead of the real address mask when
193 the system replies to an ICMP Address Mask Request packet.
197 Enable/disable replies to ICMP Address Mask Request packets.
201 Number of bytes from original packet to quote in ICMP reply.
202 This number is internally enforced to be at least 8 bytes (per RFC792)
203 and at most the maximal space left in the ICMP reply mbuf.
206 Delay in seconds before expiring route created by ICMP redirect.
207 .It Va reply_from_interface
209 Use the IP address of the interface the packet came in through for
210 responses to packets which are not directly addressed to us.
211 If enabled, this rule is processed before all others.
212 By default, continue with normal source selection.
213 Enabling this option is particularly useful on routers because it
214 makes external traceroutes show the actual path a packet has taken
215 instead of the possibly different return path.
218 An interface name used for the ICMP reply source in response to packets
219 which are not directly addressed to us.
220 By default continue with normal source selection.
223 Enable/disable replies to ICMP Timestamp packets.
227 A socket operation may fail with one of the following errors returned:
230 when trying to establish a connection on a socket which
231 already has one, or when trying to send a datagram with the destination
232 address specified and the socket is already connected;
234 when trying to send a datagram, but
235 no destination address is specified, and the socket has not been
238 when the system runs out of memory for
239 an internal data structure;
240 .It Bq Er EADDRNOTAVAIL
241 when an attempt is made to create a
242 socket with a network address for which no network interface
257 protocol implementation appeared in